A tire having a radial carcass reinforcement in known manner comprises a tread, two inextensible beads, two sidewalls joining the beads to the tread and a belt arranged circumferentially between the carcass reinforcement and the tread, this belt being formed of various plies (or “layers”) of rubber which may or may not be reinforced by reinforcement elements (“reinforcing threads”) such as cables or monofilaments, of the metallic or textile type.
The tire belt is generally formed of at least two superposed belt plies, sometimes referred to as “working” plies or “crossed” plies, the generally metallic reinforcement cables of which are arranged in practice parallel to one another within a ply, but crossed from one ply to the other, that is to say inclined, whether symmetrically or not, relative to the median circumferential plane, by an angle which is generally of between 10° and 45° depending on the type of tire in question. The crossed plies may be finished off by various other plies or auxiliary layers of rubber, of widths which are variable depending on the case, and which may or may not comprise reinforcing threads; mention will be made by way of example of simple cushions of rubber, what are called “protective” plies, the role of which is to protect the rest of the belt from external attack and perforations, or alternatively what are called “hooping” plies comprising reinforcing threads oriented substantially in the circumferential direction (what are called “zero-degree” plies), be they radially external or internal relative to the crossed plies.
A tire belt must in known manner fulfil various demands, which are frequently contradictory, in particular:                be as rigid as possible at low deformation, because it contributes substantially to stiffening the crown of the tire;        have a hysteresis which is as low as possible, in order on one hand to minimise the heating during travel of the inner zone of the crown and on the other hand to reduce the rolling resistance of the tire, which is synonymous with saving fuel;        finally have high endurance, with respect in particular to the phenomenon of separation, cracking of the ends of the crossed plies in the shoulder zone of the tire, known by the name “cleavage”, which requires in particular the metal cables which reinforce the belt plies to have high fatigue strength in compression, all in a more or less corrosive atmosphere.        
The third demand is particularly strong for heavy-vehicle tires, designed to be able to be retreaded one or more times when the treads which they comprise reach a critical degree of wear after prolonged travel.
For the reinforcement of the belts above, generally steel cables (“steel cords”) referred to as “layered” (“layered cords”), formed of a central core and one or more concentric layers of wires arranged around this core, are used. The layered cables most used are essentially cables of construction M+N or M+N+P, formed in known manner of a core of M wire(s) surrounded by at least one layer of N wires, possibly itself surrounded by an outer layer of P wires.
The availability of carbon steels which are becoming ever stronger and more enduring, in particular, means that tire manufacturers nowadays, as much as possible, are tending towards the use of cables having only two layers, in order in particular to simplify the manufacture of these cables, reduce the thickness of the composite reinforcement plies, and ultimately reduce the costs of the tires themselves.
The two-layer cables essentially used hitherto in the belts of tires are essentially cables of construction 2+7, 3+8 and 3+9, formed of a core or centre of 2 or 3 wires and an outer layer of N wires (respectively 7, 8 or 9 wires) which is more or less unsaturated owing to the large diameter of the core produced by the presence of the two or three core wires.
It is known that this type of construction promotes the ability of the cable to be penetrated from the outside by the calendering rubber of the tire or of the rubber article during the curing of the latter, and consequently makes it possible to improve the endurance of the layered cables in terms of fatigue and fatigue-corrosion, particularly with respect to the problem of cleavage mentioned previously.
These 2+7, 3+8 and 3+9 cables are however not without drawbacks.
Cables of construction 3+8 and 3+9 cannot be penetrated as far as the core owing to the presence of a channel or capillary at the centre of the three core wires, which remains empty after impregnation by the rubber, and therefore favourable to the propagation of corrosive media such as water. As for 2+7 cables, as furthermore with the previous ones, they are still relatively bulky with a low strength per unit of section owing to their unsaturated outer layer.
Furthermore, one major objective of a tire manufacturer wishing to reduce the hysteresis of the belts of tires is nowadays to reduce the thickness of the composite reinforcement fabrics used in these belts, in particular owing to the use of highly compact cables.
In continuing their research, the Applicants have discovered a novel layered cable, of construction 1+N, rubberized in situ, which not only has increased resistance to corrosion, but also and above all imparts improved endurance in compression to the belts of the tires. The longevity of the tires and that of their crown reinforcements is thus significantly improved, very particularly with regard to the phenomenon of cleavage previously explained.